1) Field of the Invention
The present invention relates to composite materials and, more particularly, relates to the forming of a composite workpiece by inductively heating the workpiece and applying pressure thereto.
2) Description of Related Art
Composite materials typically include a fibrous material such as graphite that is impregnated with a matrix material. The fibrous material is generally strong and stiff and is held in place by the matrix material, which can be formed of a thermoplastic resin, a thermoset resin, or a metal. In combination, the fiber and matrix can provide a strong, stiff, lightweight material, which can also have specific dimensional properties. Examples of composite materials include alumina-, boron-, or silicon carbide-based fibers provided in a weave, braid, or non-woven arrangement and combined with a matrix formed of Ultem® polyetherimide (PEI) resin, a registered trademark of General Electric Company, or other thermoplastic resins such as poly ether-ether ketone (PEEK) or poly phenylene sulphide (PES). Composites can also include a matrix formed of metal, such as titanium or aluminum, or a graphite composite with an insert of titanium or aluminum metal foil to create a fiber-metal composite laminate.
According to one conventional method of manufacturing a composite member, tapes of the fibrous material that are preimpregnated with the matrix material are disposed on a mandrel or mold that defines the desired shape of the finished member. The preimpregnated tapes are then heated on the mandrel and consolidated against the mandrel. This method is generally time consuming, and often results in wasted materials such as the plaster mandrel.
Alternatively, composite laminates can be manufactured as a flat sheet, and subsequently formed to the desired shape. For example, the flat sheet can be inserted between one or more metal tools with contoured surfaces that define the desired shape of the sheet. The tools are heated, for example, using an oven or other heating device. Thermal energy is conducted from the tools to the composite sheet to heat the sheet to a forming temperature at which the tools can mold, or urge, the sheet to the desired shape. The tools are cooled with the formed composite sheet therebetween, and the sheet is then removed. The time and energy required for heating and cooling the tools adds to the expense of the manufacturing process.
Thus, there exists a need for an improved apparatus and method for forming a composite material. The apparatus and method should be capable of heating and cooling the composite material quickly to a temperature sufficient for consolidation, and preferably should not require that large supporting tool members be heated and cooled during each cycle.